The cement industry is a mass-production/mass-consumption type industry for which it is assumed that resource saving and energy saving have been and will be the most important issues. For example, to manufacture Portland cement which is now manufactured in largest quantity, raw materials which have been prepared to achieve predetermined chemical composition must be sintered at a high temperature of 1,450 to 1,550° C. to produce a clinker, and energy costs for obtaining this temperature are huge.
Meanwhile, effective use of waste products and by-products is now an important issue in connection with a recent global environmental problem. Making use of the characteristic features of the cement industry and the cement production equipment in order to make effective use of or dispose of waste products as raw materials or fuel for the manufacture of cement is considered as effective because large amounts of waste products can be disposed of safely (Patent Document 1).